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June 11, 2014 -- A substance found in a variety of plant-based foods may improve blood sugar in people at risk for heart disease and diabetes, according to a recent study.

Researchers found that a diet rich in plant antioxidants (called polyphenols) lowered blood sugar. The antioxidants are found in dark chocolate, green tea, coffee, and extra virgin olive oil, among other foods.

Lead researcher Lutgarda Bozzetto, MD, says the people in the study felt the diet was easy to stick with. Bozzetto is with the University of Naples Federico II in Italy and presented the study at the European Atherosclerosis Society 2014 Congress.

"It's a diet that is realistic for these high-risk patients," she tells Medscape.

Study after study has touted the benefits of coffee, green tea, and dark chocolate. The antioxidants found in these foods may help lower the risk of heart disease and diabetes, prevent certain cancers, and even help the brain.

Early studies have shown that diets rich in polyphenols may help improve how your body metabolizes sugar, Bozzetto says.

In this new study, 45 overweight or obese people followed one of four diets:

A diet low in omega-3 fatty acids and polyphenols (consistent with the typical American diet)

A diet rich in omega-3 fatty acids

A diet rich in polyphenols

A diet that included omega-3 fatty acids and polyphenols (in lower amounts than group 3)

Those on the omega-3 fatty acid-enriched diets lost more weight during the 8-week study. But blood sugar and insulin levels improved more with the polyphenol-enriched diet. The researchers also noticed improvements in the way the pancreas worked in people on the polyphenol-enriched diet.

Bozzetto says this effect of polyphenols is similar to many diabetes medicines. And it may not only help treat diabetes, but may also help prevent it. More research is needed, but a diet rich in plant antioxidants is chock-full of healthy nutrients.